The present invention relates to an image-separating point detecting process for separating only a subject image from images having gradation and an image separating apparatus using the same and in particular to a method for detecting points to separate a specific subject image from multi-color natural images which are picked up by a television camera and an image separating system.
An image synthesizing technique for merging a given subject image in one scene into another image background scene and the like has heretofore been used in the process for preparation of a picture such as movie or commercial poster. The commercial image synthesizing technique includes two approaches as follows:
(a) A screen projection approach. An image which will become a background is projected on a screen and a given subject or object is placed before the screen and the image of the given subject is picked up together with the background.
(b) A chromakey synthesizing approach. A single background (usually referred to as blue back) is used at the time of editing. The image of a given subject is extracted on the basis of the difference in color components of the given subject and the background and is merged into the other image (background). In both methods, a special apparatus has to be used for picture taking. It is hard to merge an image which has previously been picked up with the other different background scene.
In other words, in order to achieve image synthesizing for an image which has been picked up, this synthesizing should be carried out in the editing phase.
Recently, home video cameras have become popular. There may be a need to remove a redundant image from a number of images which were picked up in the background, or to conduct editing for synthesizing the image of a person with a special background. Also in this case, much effort is necessary since such editing is performed manually for every image of a motion picture.
As one of a plurality of editing functions, an operation to automatically extract a given subject from taken images is required.
(a) A method for separating a given subject image which is performed by a computer has been proposed in, for example, "SNAKES: Active Contour Models" (Proc. ICCV-87, PP. 259 to 268, 1987). The method comprises modelling the contour of a subject based upon the features of the subject, defining the contour as a function and inferring the contour in the vicinity of an initial input by determining the contour in accordance with the features of the preliminarily defined function even if a part of the contour of the subject is not clear.
(b) A technique to separate a motion subject by determining differences between the frames of motion picture is disclosed in, for example, "Development of Video Surveillance System using Motion Information" (October National Convention Summary Record of the Institute of Electronics and Communication Engineers of Japan, page 7-178, 1991). First, differences between frames are determined by performing a linear operation for each pixel of the image over continuous frames. Thereafter, the points of changes are used to trace a locus of a moving subject for separating a given subject image.
(c) A system for separating a given subject image by using color information of image is disclosed in, for example, JP-B-2-4027. In this system, a histogram is determined by performing a color linear operation for each pixel and then a given subject image is separated by thresholding the results.